Loading system



J. MILLS LOADING SYSTEM Sept. 15, 192.4. 5 1,508,565

. Filed March 29. 1923 fiy/ //7 yen/0n John /7///J Improvements inLoading Systems,

Patented Sept. 16, 1924..

UN IT D S TE JQHN .IVIILLS, or wyomine, amnesty,assrcnortaownsrpaivannotate coi/i]- ma mcoaroaaran, or NEW YORK, N. 2.,.AQOBPQRATIQ YD NEW $03 LOA ING SYSTEM.

To all whom it may concern, I

Be-itlknown'that I, J OHN MILLS, a citizen of -the United States,residing at Wyoming,

in the county of Essex, State of New Jer sey, have invented-certain newand useful Which-the ifollowingis a-full, clear, concise,

ZLIl'Cl BXtLGt description.

'This invention relates to'communication over loa'ded dines and'ha's foran object'yto improve the transmission of signals, voice currents :inparticular, over loaded lines.

The advantages of light loaded telea phone lines having a "high naturalcut off frequency have been pointed out in thespplication'of Carson,Clark and-Mills, Serial fects dueto unequal rates of propagation of thevarious frequencies of importance 1n speech. The important voicefrequencies may be taken to'be included in the range well known thatsatisfactory speech transmission may be had witlra range considerablysmaller than this. fF-req uencies higher than 2500 vcyclesoare presentin speech and aidintelligibi-lity if they can be transmitted withoutdistortion. In long lines, however, even if extra light loaded, the timerequired for transmission of thehigher frequencies may be relatively sogreat that the resulting distortion or so called transient effects mayoutweigh the advantages of having these frequencies transmitted.

In accordance with this invention substantially uniform speed oftransmission of the important voice frequencies is obtained by usinghigh cut off light-loaded lines and the distorting efiect of the higherfrequencies is eliminated by preventing them from reaching the receivingstation. The cut off frequency of the line should be substantially abovethe highest frequency to be utilized in speech transmission and withcertain lengths of line should be twice as great or more. The upperspeech frequencies may be suppressed by any suitable means such aslow-pass wave-filters which may be located at repeater stations or atany suitable point or points between a transmitter at one end of theline and a receiver at the other end.

The invention will be more fully understood from the followingdescription and cla-imstaken in connection with the accompanyingdrawings in which: i

Fig. 1 illustrates graphically a -.fundamental characteristic of aloaded line, and

Fig. 2 illustrates schematicallya portion of a system embodying theinvention. The curve in Fig.1 shows the rel'ative time of transmissionof the" various fre quencies on a loadedline' up to its cutofffrequency. The abscissa: are given in terms fi h vi a t i Wlii -f ap -sa equ ncy a a var abl and f; .KQP QIS it the cut off frequency. "Theordinates are given I asla function of according to the as varia e -.an:iairepres nt th t me Of ra mission o zer fr qu ncy Th equ fraction 1 t-t sin f/fg i f/fo' Itiwillbe. seen that .overa frequency range from 0vto betWeen*0.6 and.:O.'7 of the entire range. .up to. the cut off .1frequency, the gliderence in I retardationonly attains about} .10 butfor frequencies closeztothe cut.- off frequency it increases rapidly andmay become as great as 50% or more. In units of time the disparity intime of transmission will of course be greater for long lines than forshort lines. Hence, for voice transmission it may be that there will bea net improve ment by omitting these higher and much retarded frequencycomponents.

In Fig. 2 is shown a system of the four wire type in which a substationS is con nected by a two wire line 10 and a balanced transformer 12 tothe unidirectional lines 14 and 16. The artificial line N performs theusual function of preventing any substantial amount of feed back fromline 16 to line 14. A similar arrangement (not shown) terminates thedistant end of the four wire circuit.

The line 14 is provided with any desired number of repeaters such asshown at It and R and the line 16 is provided with oppositely directedrepeaters R R etc. The lines 14 and 16 which may be small gau e cablelines are provided with loading coi s 20 of such values and spacing thatthe lines have a high critical orcut 01f frequency, say

in which 2i; represents time I 5600 cycles. Reference to Fig. 1 willshow that if the critical frequency of the line is 5600 cycles, the timeof transmission of frequencies below 2500 cycles will be fairl uniform.Low pass filters indicated at 1 and F are accordingly provided tosuppress the speech frequencies above 2500 cycles or at least to reducetheir amplitude at the receiving station to a harmless value.

While the invention has been described as applied to a four wire system,it obviously is adapted for use in other types of systems and maybeapplied thereto in a great variety of manners Within the scope of theappended claims. 1

The invention claimed is:

1. A telephonev system comprising a loaded line having a criticalfrequency such that the higher speech frequencies are transmittedsubstantially slower than the frequencies of principal importance tointelligibility and means for reducing the efficiency of transmission ofsaid higher frequencies.

2. A telephone system comprising a loaded line having a criticalfrequency such that the higher speech frequencies are transmittedsubstantially slower than thefrequencies of principal importance tointelligibility and means for reducing the efliciency of transmission ofsaid higher frequencies, the range of frequencies having theirtransmission reduced being at least one third as great as the range offrequencies freely transmitted.

3. A telephone system comprising a loaded line having a criticalfrequency such that the higher speech frequencies are transmittedsubstantially sloWer than the frequencies of principal importance tointelligibility and a wave filter for attenuating said higherfrequencies.

4. A telephone system comprising a loaded line having a criticalfrequency such that the higher speech frequencies are transmittedsubstantially slower than the frequencies of principal importance tointelligibility and a wave filter for attenuating said higherfrequencies, said wave filter havlng a cut off frequency of the order ofone half said critical frequency.

5. A telephone system comprisinga loaded line having a criticalfrequency of the order of6000 cycles and means for substantiallysuppressing speech currents above a frequency of the order of 2500cycles.

6. A telephone system comprising a loaded line having a criticalfrequency of the order of 6000 cycles, means for supplying speechcurrents to said line, and a low pass filter in said system in the pathof said speech currents and having a cut off frequency of the order of2500 cycles.

7 A telephone system comprlsing a loaded line having a criticalfrequency such that the higher speech frequencies are transmittedsubstantially slower than the frequencies of principal importance tointelligibility and having a length such that the actual time lag ofsaid higher frequencies is substantial, and a wave filter forattenuating said higher frequencies, said wave filter having a cut offfrequency sufiiciently lower than said critical frequency to produce anet gain in intelligibility. y

In witness whereof, I hereunto subscribe my name this 20 day of March,A. D. 1923 JOHN MILLS

